A related art is disclosed in Japanese Patent Publication 2002-91549 which is a failure diagnosis device of an electronic control system for a vehicle. This failure diagnosis device has a signal analysis portion for analyzing communication signal information that is received through an input portion provided in the failure diagnosis device from a multiplex communication line to which a plurality of electronic control related members are connected.
The signal analysis portion includes a first failure region identification portion that identifies an area with a possibility of failure in a multiplex communication system such as a sensor failure, or the like based on whether or not communication is performed by the plurality of electronic control related members using the received communication signal information; and a second failure region identification portion that identifies an electronic control related member with a possibility of failure out of the plurality of electronic control related members based on data contents of the communication signal that is obtained from the communication signal information.
Accordingly, it is possible to identify the area with a possibility of failure in the multiplex communication system, and the electronic control related member with a possibility of failure out of the plurality of electronic control related members.
However, in the related art as disclosed above, for example, when it is determined that there is an abnormality with the multiplex communication system, the abnormality portion of the multiplex communication system cannot be identified. That is, the first failure region identification portion performs failure diagnosis for the entire multiplex communication system. Therefore, only a board failure region such as a sensor failure, or the like can be identified, and a determination cannot be made what kind of abnormalities has occurred at which portion of the multiplex communication system. (It is not possible to determine whether an abnormality has occurred in a main line of the multiplex communication line, or a branch line that is wired from the main line to the electronic control related members, and in the latter case at which a branch line abnormality has occurred.)